Electronics and Communication Engineering - Power Electronics

21. 

In brushless excitation system of modern alternators, the main exciter is

A. dc generator
B. ac generator
C. either dc or ac generator
D. induction generator

Answer: Option B

Explanation:

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22. 

The two-transistor model of a thyristor consists of two transistors :

A. one n-p-n and other p-n-p
B. both p-n-p
C. both n-p-n
D. one n-p-n and other UJT

Answer: Option A

Explanation:

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23. 

In a thyristor, the forward breakover voltage

A. is constant
B. may be constant or may depend on gate current
C. decreases as gate current is increased
D. increases as gate current is increased

Answer: Option C

Explanation:

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24. 

The gate lead, in a thyristor is welded to :

A. p layer to which anode is connected
B. n layer nearest to the anode terminal
C. p layer nearest to the cathode terminal
D. outside n layer

Answer: Option B

Explanation:

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25. 

In a 3 phase full converter, the firing angle is less than 60°. The instantaneous output voltage

A. will have positive part only
B. will have both positive and negative parts
C. may have both positive and negative parts
D. will have negative part if load is inductive

Answer: Option A

Explanation:

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